Fluorescent lamp



A ril 11, 1944. K. v. GESSEL FLUORESCENT LAM;

Filed May 12, 1942 K4RELVAN GEssEz,

INVENTOR.

iz. m/lw% ATTORNEY Patented Apr. 11, 1944 i 2,348,522 FLUORESCENT LAMPKarel Van Gessel, New York, N. Y., assiznor to Hartford National Bankand Trust Company, Hartford, Conn., as trustee Application May 12, 1942,Serial No. 442,669

. 3 Claims. (Cl. 176-122) The present invention relates to fluorescentelectric discharge lamps and more particularly to an improvedfluorescent lamp characterized by a high operating efflciency.

In their usual form fluorescent lamps comprise a sealed cylindricaltubular envelope the interior surface of which is coated with afluorescent material, and means to generate invisible ultra-violetradiations which impinge on the fluorescent coating and are convertedinto visible radiations. As the source of ultraviolet radiations, agaseous discharge is used, and for this purpose the envelope contains agaseous filling and is provided with suitable electrodes for startingand maintaining the discharge. In practice, mercury vapor is used as thedischarge gas and the quantity thereof is regulatedso that at theoperating temperature theultra-violet ra-. diations generated fallpredominantly within the spectral range of about 2537 Angstrom units atwhich wave length the most generally used fluorescent materials exhibittheir greatest sen sitivity. To the mercury vapor there may be added asuitable inert gas such as argon or neon, or a mixture thereof, tofacilitate the 7 starting of the discharge.

It is an object of the invention to provide a fluorescent lamp'in whichsubstantially all of the invisible radiations of the discharge areconverted into visible light.

A further object of the invention is to provide a fluorescent lamp ofgreater efficiency than could heretofore be obtained.

These and further objects of my invention will appear as thespecification progresses.

In accordance with the invention, the lightconversion efiiciency of afluorescent lamp is increased by establishing a high ratio between thearea of the fluorescent material exposed to the gaseous discharge andthe volume of the discharge space, and hence the electrical energysupplied to the fluorescent lamp.

It is a further feature of the invention that the said high ratiobetween the area of the material exposed to the discharge and the volumeof the discharge, is obtained by a construction which is simple tomanufacture and of low cost.

The invention will be described in greater detail with reference to theappended drawing forming part of the specification and in which:

Figure 1 shows partly in cross-section a fluorescent lamp in accordancewith the invention.

Fig. 2 is a cross-sectional view taken along the line 2-2 of Fig. 1.

Fig. 3 is a cross-sectional view of a second embodiment of a fluorescentlamp in accordance with the invention.

Fig. 4 is a cross-sectional view of another embodiment in accordancewith the invention.

Referring to Fig. l, the lamp there shown comprises a cylindrical glasstube iii having its interior surface coated or lined with a suitablefluorescent material it. Concentrically arranged within the tube it is asecond glass tube ll having its outer surface coated with a fluorescentlayer it. Coatings it and it are applied to the tubes in and ii in knownmanner, for example, by painting or spraying the tubes with a suitablesuspension of the fluorescent material in finely divided form, or byimmersing the tubes in such a suspension. Suitable fluorescent materialsmay include for example, magnesium tungstate, zinc orthosilicate, zincberyllium silicats and calcium tungstate. Other suitable fluorescentmaterials will immediately suggest themselves to those skilled in theart and a further reference to the same is believed to be unnecessary.

Tubes it and i i are sealed together at their end portions to form anannular cylindrical discharge space 52 within which is provided ameasured amount of mercury vapor and a mixture of neon gas and argongas.

Electrodes i5i5 provided at opposite ends of the discharge space servefor starting and maintaining the discharge, said electrodes being formedpreferably with an annular shape and surrounding the ends of the tube iito thereby bring about a uniformly distributed discharge through thespace it. As shown in the drawing (see Fig. 2), each electrode consistsof two helical filaments connected in parallel, and in practice theelectrodes are coated with an elec tron-emissive material such as bariumoxide, strontium oxide or the like to facilitate the starting of thedischarge. External electrical connections to the electrodes lid-i5 areprovided by suitable lead-in wires (not shown) connected to theelectrodes and to connecting pins ii-El and l8-l8 respectively, whichpins also serve as mounting members for the lamp.

The external, electrical circuit for operating the fluorescent lamp isof the type well known in the art and a description of the same isbelieved to be unnecessary.

The novel construction above described brings about substantialincreases in the surface area of the fluorescent material exposed to thedischarge in a simple and economical manner. Furthermore, the ratiobetween the surface area oi the fluorescent material and the dischargevolume is readily and simply adjusted within any desired value merely bycontrolling the diameter of tube Thus by increasing the diameter of tubeM an increase in the surface area of the fluorescent material and also;adecrease in the volume of the discharge space is obtained.

Another advantage of the construction of the invention is that theultra-violet radiations are generated immediately adjacent to thefluorescent layers, and since the radiations travel only a minimumdistance from their point of origin before exciting the fluorescentmaterial, there is substantially no reabsorption of the radiations bythe discharge gas.

A further advantage of the construction of the invention is that itmakes possible light sources of heretofore unavailable color-ranges andcolorblends. For example, new color blends may be obtained byconstituting the coating l3 of a fluorescent material of a particularcharacteristic colorand the coating I4 of a material of a differentcharacteristic color.

For even further increasing the efflciency of the fluorescent lamp theinner surface of the tube H is provided with a suitable reflecting layerof silver, aluminum or the like, such a reflecting layer being shown asI9 in Figs. 1 and 2.

The principles of above described construction may also be applied tofluorescent lamps having high values of light output and in Fig. 3 suchan embodiment of the invention is illustrated.

The lamp there shown comprises a cylindrical glass tube 20 the interiorsurface of which is provided with a coating 2| of fluorescent material.concentrically arranged within tube 20 is a glass tube 22 having itsouter and inner surfaces provided with fluorescent coatings respectively23 and 24. Coatings 2|, 23. and 24 may be applied to the surfaces of thetubesl2|l and 22 in known manner as previously pointed out.

The tubes 20 and 22 are sealed and joined together at their end portionsto form an annular cylindrical discharge space 25, and a cylindricaldischarge space 26. Each of the discharge spaces contains a gaseousfilling, for example, of mercury vapor small amount of neon and argon.

For starting and maintaining a discharge within the space 25, annularshaped electrodes 21-21 conforming to the requirements of the electrodes|5|5 of Figs. 1 and 2, are provided at each end of the discharge space.Similarly, for starting and maintaining a discharge within the space 28these are provided at the opposite ends thereof,

electrodes 28-28 which for the reasons previously pointed out are alsopreferably of the coated flla me'ntary type.

The fluorescent lamp illustrated in Fig. 4 comprises an envelope havingtwo concentric conically shaped wall portions 3| and 32 sealed togetherat their base and apex portions to form an annular discharge space 33.Upon opposing surfaces of the portions 3| and 32 are fluorescentcoatings 34 and 35 respectively and withinthe discharge space is afilling of mercury vapor and a small amount of neon and/or other insertgas. At opposite ends of the discharge space there are providedelectrodes 36'3| consisting preferably of annular helically-woundfilaments coated with a suitable electron emissive material tofacilitate the starting of the discharge. External electricalconnections to the electrodes are made at diametrically oppositeportions thereof by metal pins 3B38 and 39-39 respectively, which aresealed into the envelope and the inner ends of which position andsupport the electrodes.

In the embodiment of the invention illustrated in Fig. 4 the lightgenerated by the fluorescent coatings 34 and 35 difluses directly fromall surfaces of the envelope. It is also a novel feature of thisconstruction that the lamp need only be mounted on a suitable pedestalto form a. "reading-lamp and the need of auxiliary equipment such as theusual lamp shade is dispensed with.

While I have described my invention in specific embodiments and byspecific examples, I do not wish to be limited thereto as obviousmodifications will occur to those skilled in the art without departingfrom the spirit and scope of the invention.

What I claim is:

1. A gaseous electric discharge lamp comprising an envelope having twosubstantially arallel concentric conically shaped wall portions joinedtogetherat their apex and base portions to fdrm a truncated annulardischarge space, a gaseous medium within said discharge space forgeneratirig high intensity radiations within the invisible portions ofthe spectrum, two annular shaped electrodes for ionizing the gaseousmedium, one of said electrodes being positioned at the apex portion ofthe discharge space and the other of said electrodes being positioned atthe base portion of the discharge space, and coatings of fluorescentmaterial on the opposing surfaces of the wall portions and exposed to.the discharge space.

, 2. A gaseous electric discharge lamp comprising an envelope having twosubstantially parallel concentric conically shaped wall portions joinedtogether at their apex and base portions to form a truncated annulardischarge space, a gaseous medium within said discharge space forgenerating high intensity radiations within the invisible portions ofthe spectrum, two annular shaped electrodes for ionizing the gaseousmedium, one of said electrodes being positioned at the apex portion ofthe discharge space and the other of said electrodes being positioned atthe base portion of the discharge space, a coating of a fluorescentmaterial having one color characteristic on the surface of one of saidwall portions exposed to the discharge space and a coating of afluorescent material having a color characteristic different from thatof said first coating on the surface of the other of said wall portionsexposed to the discharge space.

3. A gaseous electric discharge lamp comprising an envelope having twosubstantially parallel concentric conically shaped wall portions joinedtogether at their apex'and base portions to form a truncated annulardischarge space, a gaseous medium within said discharge space forgenerating high intensity radiations within the invisible portions ofthe spectrum, two electrodes for ionizing the gaseous medium eachcomprising a helical filamentary member arranged in annular form,terminal members connected to each filamentary member at diametricallyopposite portions thereof, one of said electrodes being positioned atthe apex portion of the discharge space and the other of said electrodesbeing positioned at the base portion of the discharge space, andcoatings of fluorescent material on the opposing surface of the wallportions and exposed to the discharge space. KAREL VAN GESSEL.

